drm/radeon: fix user ptr race condition

Port of amdgpu patch 9298e52f8b51d1e4acd68f502832f3a97f8cf892.

Signed-off-by: Christian König <[e-mail]>
CC: [e-mail]
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/radeon_gem.c

···
 	if (robj) {
 		if (robj->gem_base.import_attach)
 			drm_prime_gem_destroy(&robj->gem_base, robj->tbo.sg);
+		radeon_mn_unregister(robj);
 		radeon_bo_unref(&robj);
 	}
 }

drivers/gpu/drm/radeon/radeon_object.c

···
 	bo = container_of(tbo, struct radeon_bo, tbo);
 
 	radeon_update_memory_usage(bo, bo->tbo.mem.mem_type, -1);
-	radeon_mn_unregister(bo);
 
 	mutex_lock(&bo->rdev->gem.mutex);
 	list_del_init(&bo->list);